|
Hello all ,
Here follows my experience with a big
loop:
I have a small loop with 40turns, the turns are
spaced 5mm and the side of the loop is 70x70cm. The wire has a diameter of
1mm. The inductance is 1.85mH and the Q is 110. Together with this I use a
modified version of the preamp described on page 30 in the LF Experimenters
Handbook. The main difference being BF246C (high current FET:s) used
instead of 2N3819.
The directivity is as follows: When
adjusted to get maximum signal from DCF39 I have about S9+30dB on the S-meter
(on a DRAKE TR7) dropping to around S7 when adjusted to get minimum
signal from DCF. (I have no means of calibrating the S-meter
accurately).
Last summer I tried a bigger loop with 6 turns and
a side of 5m. It was mounted with the lowest corner about 50cm above ground and
using the same preamp as described above. The wire used was with a cross section
of 1,5mm2 and having plastic insulation.
It was then turned to get a peak on DCF39.
Changing between the two loops a few times revealed that the big loop was just
slightly better than the small loop. The difference was barely detectable on the
S-meter. I did not measure the Q, however when adjusting for resonance I found
that it was not that "sharp" as that of the small loop so the Q seems to
be lower. The inductance was around 1mH. Considering the small difference
to the samll loop and the problem of turning it I soon took it
down.
Merry Christmas and a Happy New Year
SM5EUF /
Urban
| 